Torque rods are used to stabilize an axle by transforming motion. They prevent the axle from spinning, prevent fore-aft movements during braking and accelerations, and they prevent axle yaw. Truck, trailer and bus suspensions also utilize torque rods to secure a drive axle to the vehicle's frame. Torque rods are used both as transverse rods to secure the drive axle to a vehicle's frame and as longitudinal rods to attach the suspension system to the vehicle axle. By securing the drive axle to the vehicle's frame using a torque rod, the drive axle's alignment to the vehicle's frame is maintained, and the proper suspension geometry for the vehicle is also maintained, so that free suspension movement is allowed by transferring torque created by the suspension movement on irregular terrain. The longitudinal connection of the suspension system to the axle helps in aligning the axle and acts as a kinematic chain.
Straight arm torque rods have been constructed using any of a welded tube design, cast design, welded solid rod design, or other designs like single piece forged designs. Typically, multiple welds are needed. Three-piece designs were also available with two solid rods welded to the end housings and an intermediate pipe, used to join the pieces together. The bushing ends have been constructed using cartridge type bushings, bonded bushings and also using other polymer designs.
Due to varying operating conditions for vehicles, severe impact loads combined with road vibrations on the suspension cause the components of the suspension, including the torque rods, to be subjected to wear. Dynamic loading conditions can accelerate wear of suspension system components and also lead to fatigue of the vehicle's operator, which may lead to premature failure of several components including torque rods.
There are two primary designs used for torque rods. The first design is a straight arm torque rod with pivot bushings on either end. The second design is the use of wishbone shaped (V-shaped) torque rods with pivotal bushings at the apex and either end of the legs. This latter design controls both fore-aft movements as well as lateral movements. Each application of a torque rod requires a rod that meets the specific needs of that particular vehicle. Because different vehicles require different torque rods, the manufacturing process results in various rods for the various vehicles. Often, mechanics installing torque rods need to cut them for fit, and once cut need to weld the pieces together. Often, multiple cuts and welds are needed. In addition, torque rods in use can fracture or break due to loads or because of wear. Wear may result from poor welds or from abrasives or other contaminants entering the area of the bearings. It would be advantageous to design a torque rod which can sustain high loads while in use, includes protection against excess wear, which can be readily replicated in manufacture, and also be used on a variety of vehicles requiring different length torque rods.